1. Field of the Invention
The present disclosure relates to conveyance of mixed flows of particles and gas, and more particularly to variable orifices such as used in coal piping systems.
2. Description of Related Art
A variety of devices and methods are known in the art for conveying flows of gas laden with solid particles. Of such devices, many are directed to coal piping systems, wherein solid particles of pulverized coal are conveyed in an air stream through a piping system such as for delivery to a nozzle for combustion in a furnace. Typical coal piping systems provide multiple parallel pipes between one or more pulverizers and the furnace. It is typically desirable for the air flow in various pipes to be uniformly distributed. For example, downstream of a split where one coal pipe feeds into two or more coal pipes downstream, it is desirable to balance the flow evenly across all of the downstream pipes in order to provide uniform combustion in the furnace. Uniform combustion produces fewer pollutants than non-uniform combustion where local imbalances in the fuel to air ratio lead to inefficient combustion and increased pollutants.
Conventional solutions to the problem of balancing flow among coal pipes have included placing variable orifices in the coal pipes. This allows regulation of pressure between pipes by constricting or obstructing part of the flow passage through the variable orifice in one or more pipes as needed. Typical variable orifice designs are butterfly valve type variable orifices or slide gate valve type variable orifices. While these devices are useful for evening pressure from pipe to pipe, they are limited in their ability to produce uniform distribution. Both butterfly valve and slide gate valve type variable orifices produce an asymmetrical imbalance in the air and particle flow downstream of the variable orifice. In other words, traditional variable orifices produce local non-uniformities in coal particle distribution within individual pipes. Non-uniform distribution of air and particles causes localized erosion of coal pipes which can eventually erode completely if not checked, creating unsafe operations.
Such conventional methods and systems have generally been considered satisfactory for their intended purpose. However, there is still a need in the art for improved variable orifices. The present disclosure provides a solution for this need.